Tractor for maneuvering an airplane without a tow bar

ABSTRACT

In the use of a tractor to maneuver an airplane on its nose landing gear, which tractor includes a chassis (10); having a rear access (32) which receives said nose wheels and having two telescoping bars (38) the length of which can be adjusted by means of first hydraulic cylinders (40) and to the rear ends of which (38.2.1) pivotable pulling arms (54) are hingedly connected for engagement behind the nose wheels; and having a support surface (30.3) for the raising of the nose landing gear, which is performed by means of second hydraulic cylinders (44), in order to cause less wear on the nose wheels during loading and raising and to prevent damage to the tractor and/or nose landing gear in the attempt to pull said nose landing gear into the recess by means of the pulling arms, it is suggested: 
     (a) to form the chassis in two parts and to hingedly connect its front portion (10.1) with its rear portion (10.2) at a folding axis (36) and by means of the second aggregates (44) above this axis; 
     (b) to arrange the immovable portions (38.1) of the telescoping bars and the cylinders (40.1) of the first aggregates (40) on the front portion of the chassis; 
     (c) to form the support surface on an elevating shovel (30) at the level of the folding axis, which elevating shovel extends from the front portion of the chassis behind this axis into the downwardly open chassis recess behind the shovel and between the rear wheels (22); and 
     (d) to provide a holder (46) axially opposite the laterally positioned pulling arms and above the elevating shovel, which holder can be moved approximately parallel to the longitudinal axis (18) at the same time as the pulling arms by means of third hydraulic cylinders (48).

The invention relates to a tractor for maneuvering an airplane without atow bar, having: a chassis which includes a rearwardly, upwardly anddownwardly open recess, a rear portion that is forked due to the recessand has a pair of coaxially mounted, powered rear wheels, and a frontportion having two steerable and perhaps powered front wheels; a pair ofapproximately horizontal cylinders of a first hydraulic cylinder pistonaggregate that are arranged parallel to each other on the chassis andare for adjusting the length of two telescoping bars which areadjustable parallel to the respective side walls of the recess and areeach provided at their free rear ends with a hinged pulling arm, whichcan pivot through a right angle between a relatively open positionrelative to the free end of the bar parallel to the axis of the tow barand a relatively closed blocking position perpendicular to the axis ofthe tractor about a vertical axis which perpendicularly intersects theassociated tow bar axis; a support surface which is arranged on thechassis at the front end of a recess and is inclined downward toward therear and underneath to allow for the elevation of the nose landing gearwhen the pulling arms and shortened telescoping bars are in theirblocking positions; and an elevating device including a pair of secondhydraulic cylinder-piston aggregates arranged on the chassis for liftingthe nose landing gear after it has been placed adjacent to and on thesupport surface and locked in place there by means of the pulling armsmoving into their blocking positions.

In a tractor known from U.S. Pat. No. 4,225,279 (Origin: FR No.2,452,427) having the same purpose, a downwardly closed chassis recessis provided which is open upward and to the rear and which receives thenose landing gear of the airplane to be maneuvered without a tow bar ina pocket-like depression, after a flap hinged to the tractor chassisbehind the pocket has pivoted down to the tarmac at an angle like a rampand the nose landing gear has passed forward up this ramp into thepocket. To accomplish this, the tractor must back up, allowing the rearedge of the ramp to be pushed between the unbraked wheels of the noselanding gear and the tarmac, which entails high impact forces which canbe damaging to the nose landing gear, particularly the wheels, and tothe tarmac. As the nose landing gear passes relatively up and forwardover the ramp into the pocket, the weight of the nose of the airplaneproduces an increasing torque relative to the rear axle of the tractor,which tends to lift the front of the tractor. It is therefore necessaryto arrange the motor of the tractor as far forward on the chassis aspossible and/or to provide ballast there, so that the front wheels ofthe tractor do not rise from the tarmac when the nose landing gear isloaded onto the tractor. Furthermore, it is difficult to control thisloading process.

Therefore, to avoid these disadvantages, certain suitable tractors ofthe above-described type have been proposed, known from DE-OS No. 33 18077, in which (see OS FIGS. 2 and 3) the chassis recess is defined by anat least U-shaped horizontal frame that is temporarily rectangular, canbe raised and lowered by means of the elevating device, houses a brakeshoe-like support body including the support surface in its forwardportion, and the sides of which are formed by the two telescoping barsand the rear of which is formed, when it is formed, by the two pullingarms in their blocking positions, where they are rigidly connected witheach other, and in which the brake shoe-like support bodies includerespective support surfaces that slope downward toward the front andunderneath. To load the nose landing gear into the rearwardly openchassis recess of this tractor, the tractor travels backwards until itsfront support body contacts the nose wheels of the perhaps braked, butin any event stationary, airplane, whereupon the two pulling arms of thetractor are folded into their horizontal positions and are lockedtogether, thereby closing the loading frame in its rectangular shape.

The telescoping bars of the unbraked, stationary tractor can then beshortened, whereby the pulling arms are brought into contact with thenose wheels and the tractor effectively draws itself backward until itsfront support body contacts the nose wheels, whereupon the three supportbodies draw the nose gear upward when the elevating device is activated.As a result, the portions of the nose wheels located between the frontsupport body on one side and the two rear support bodies on the otherside are pressed through under the load (about 20 t.) of the nose of theairplane and are squeezed front and rear, which after many repetitionscan lead to tire damage on the nose landing gear, which may also resultby different means with the known tractor having a ramp and pocket.

While with the known tractor having a ramp and pocket there can bedifficulties in communication between the tractor driver and theairplane pilot relative to activating the nose gear brakes of theairplane before the tractor approaches, which result in the danger ofunintentional movements of the airplane or damage to the nose landinggear and/or the tractor, such difficulties do not exist with the knowntractor of the above-described type, at least when such a tractorapproaches a braked airplane which, however, can also be unbraked.

The object of the invention is to create a tractor for maneuvering anairplane with its nose landing gear which avoids the cited disadvantagesof the two known tractors, and which does not unduly cause damage to thenose wheel tires of the airplane as the nose landing gear is beingloaded by the tractor and raised and which reliably prevents damagethereto and to itself caused by delayed pressurization of the landinggear brakes of the airplane.

This object is achieved according to the invention with a tractor of theabove-described type, in that: the front and rear portions of thechassis are separate and are hingedly connected with each other by meansof a single jointed axle running parallel to the rear axle; theapproximately horizontal second aggregates arranged parallel to thetractor axis are each connected on one end to the front portion of thechassis and on the other end to the rear portion thereof; the cylindersof the first aggregates and the immovable portions of the telescopingbars are mounted on the front portion of the chassis and an elevatingshovel which includes the support surface is attached to this frontportion behind the jointed axle; and a pair of approximately horizontalcylinders of third cylinder-piston aggregates are provided parallel tothe front portion of the chassis, the piston rods of which thirdaggregate are arranged on one of the respective sides of the recess inthe chassis and are provided at their rear free ends with at least onehinged holder disposed perpendicularly to the tractor axis, which holdercontinuously projects into the recess in the chassis.

In this manner it is advantageously achieved that the nose wheel tiresof the airplane are not subjected to an unusual deformation either whenthey are taken hold of or when they are raised, because the elevatingshovel creates a replacement floor corresponding to the tarmac ontowhich the nose wheel tires can be rolled naturally; and due to thebraked condition of the tractor and the pulling of the airplane, theairplane brakes can be released from the beginning (and indeed must be),thus obviating any necessity for communication between the pilot and thedriver.

In one preferred embodiment of the tractor according to the invention,the jointed axle for hingedly connecting the front and rear portions ofthe chassis are arranged approximately at the level of the supportsurface of the elevating shovel at the front end thereof and the secondaggregates engage the rear portion of the chassis approximately over thejointed axle. This achieves a maximum elevating torque.

In the preferred embodiment the telescoping bars of the first aggregatesthat adjust them are inclined to fall toward the rear from thehorizontal, so that the pulling arms also do not press the smallerwheels of the nose landing gear of a smaller airplane down onto thetarmac, which would make it more difficult to load the nose wheels ontothe elevating shovel.

In the preferred embodiment the cylinders of the first aggregates andthe immovable portions of the telescoping bars are arranged adjacent toone another in such a manner that each cylinder and a fixed rear portionof the telescoping bars are arranged at approximately diametricallyopposite points relative to the tractor axis in the recess of thechassis, and engage the one-sided piston rods projecting from theassociated cylinders at the front ends of the movable front portions ofthe telescoping bars. In this manner, with constant pressure from thehydraulic medium, a greater pulling force is achieved than with areversed arrangement of the first aggregates relative to the telescopingbars, because of the full utilization of the piston surface. In thepreferred embodiment, respective truncated shafts serving to mount thepulling arms are provided on the free ends of the movable end portionsof the telescoping bars so as to rotate therewith. These truncatedshafts extend along the pivot axis of the respective pulling armassociated therewith and are rotatably mounted on the end of theassociated telescoping bar. Respective pivot arms connected with theirassociated truncated shafts and a cylinder of a fourth hydrauliccylinder-piston aggregate mounted on the associated movable portions ofthe telescoping bars are also provided for pivoting the pulling arms.The piston rods projecting rearwardly from these cylinders are hingedlyconnected with the ends of the associated pivot arms opposite thetruncated shafts. This makes possible a simple, remotely controllablepivoting of the pulling arms.

In the preferred embodiment, the fourth aggregates are arrangedapproximately parallel on the movable end portion of the associatedtelescoping bar, and the front end of each cylinder thereof is hinged atthat point and the piston rod thereof is hinged to a one-armed leverwhich is pivotably mounted to the end portion of the telescoping bar ata point lying closer to the pivot axle of the lever. Furthermore, oneend of a rigid coupling member is hinged to the other end of the leverat a point lying farther from its pivot axle, and the other end thereofis hingedly connected to the free end of the associated pivot arm,whereby all hinge axles are parallel to each other and are approximatelyperpendicular to the pivot axles of the associated pulling arms. As aresult, the knee lever consisting of the one-armed lever and thecoupling member, when it is extended, transfers the compression force tothe telescoping bar, so that the fourth aggregate must only maintaintheir extension and do not need to be separately loaded.

In the preferred embodiment, the pulling arms and/or holders are eachformed as roller blocks which are mounted so as to freely rotate on theassociated truncated shaft, i.e., on the free rear end of the piston rodof the associated third aggregate about an axle that is sometimes oralways horizontal. In this manner the linear contact of a single rollerwith the nose landing gear of the airplane to be towed, which is engagedbehind by a pulling arm and held down by a holder is replaced by amultiple-lined, i.e., quasi surface-like contact between the rollerblock and the nose wheel, so that the engagement and holding down alsotakes place reliably and with reduced wear on the tires even with nosewheel diameters that differ from airplane to airplane. Instead of theroller blocks, however, individual rollers can also be used, althoughcare must be taken to assure that the requisite rolling friction ispresent between the nose wheels of the airplane to be towed, on the onehand, and the pulling arms and holders of the tractor on the other hand.

In the preferred embodiment, the holders are formed as holding arms andare partially rigidly connected with each other perpendicular to thetractor axis, so that both nose wheels of the nose landing gearexperience a uniform contact over the entire width of the elevatingshovel, except the center thereof in the case of roller blocks formed asholding arms, which render a centering of the moving nose landing gearon the longitudinal axis of the stationary tractor superfluous.

The invention is described in greater detail below with the aid of thepreferred embodiment of the tractor according to the invention, examplesof which are illustrated in the drawings. Shown are:

FIGS. 1 and 1A top views of the embodiment, whereby the upper and lowerhalves show the condition before and after the loading of the airplanenose wheels;

FIG. 2 a side view of the embodiment with the imaginary wheel loading,corresponding to the upper half of FIG. 1; and

FIGS. 3 and 4 corresponding longitudinal sections, broken off at thefront end, through the embodiment as side views of the upper half inFIG. 1 before and after the imaginary wheel loading.

The tractor according to the invention includes an essentially two-piecechassis (10), on the larger, unified front portion (10.1) of which,approximately in its center, there is mounted a drivable front axle (12)having two steerable front wheels (14) and on which a cabin (16) for thetractor driver is placed in front of the front axle. The rear portion(10.2) of the chassis consists of a left half (10.2.1) and a right half(10.2.2), which are formed as mirror images of each other relative to avertical symmetry plane containing the longitudinal axis (18) of thetractor (10), which plane is perpendicular to a smooth, imaginary travelsurface (20) for the tractor, but are otherwise formed identically. Eachhalf of the rear portion of the chassis (10.2) includes a drivable rearwheel (22) which turns with the opposite second rear wheel about thesame imaginary lateral axis (24), which lies perpendicular to thevertical plane of symmetry containing the longitudinal axis (18), whichis also true for the longitudinal axis (26) of the sections of the frontaxle (12) mounted on the front portion (10.1) of the chassis. Aninternal combustion engine (28) is provided behind the front axis (26)centered in the front portion (10.1), and all wheels (14 and 22) arehydrostatically driven.

At its rear end behind the engine (28), the front portion (10.1) of thechassis has an elevating shovel (30) with a smooth lower support surface(30.1) which rises slightly toward the rear, the full surface of whichcomes into contact with the tarmac (20) when the front portion (10.1) ofthe chassis rotates about the front axis (26). The elevating shovel(30), which can pivot about the front axis (26), extends in thedirection of the longitudinal axis (18) of the tractor, which is alsocontained in the vertical plane of symmetry of the shovel, as well, backto the two rear wheels (22) and laterally to a point where its sideplates (30.2) are at a certain distance from the adjacent halves(10.2.1) or (10.2.2) of the rear portion of the chassis, which define arearwardly, upwardly and downwardly open recess (32) in this rearportion.

The front portion (10.1) and the rear portion (10.2) of the chassis arehingedly connected with each other by means of the fact that on one sidethe left half (10.2.1) of the chassis and on the other side the righthalf (10.2.2) of the rear portion of the chassis form respective swiveljoints (34), the pins of which align and define a folding axis (36)which perpendicularly crosses the longitudinal axis (18) of the tractorand runs horizontally approximately at the level of an upwardly facingsmooth support surface (30.3) of the elevating shovel (30). This foldingaxis (36) lies in front of and adjacent to a forwardly rising stopsurface (30.4) of the elevating shovel (30) which joins the supportsurface (30.3) at an angle and lies between the support surface (30.3)of the elevating shovel (30) and the engine (28).

Respective four-sided telescoping bars (38), which bridge the mentionedlateral distance are located between the side plates (30.2) of theelevating shovel on one side and the left or right halves of the rearportion (10.2) of the chassis on the other side. The fixed portions(38.1) of these telescoping bars (38) are attached to the front portion(10.1) of the chassis and extend into the recess (32) of the rearportion (10.2) of the chassis between the front wheels (14) on one sideand the rear wheels (22) on the other side approximately to the rearedge (30.5) of the elevating shovel (30), where the support surface(30.3) and stop surface (30.4) thereof join. The movable portion (38.2)of each telescoping bar is axially guided and the end section (38.2.1)thereof, even when the telescoping bars (38) are at their minimumlength, project rearwardly out of their associated fixed portions (38.1)to such an extent that they overlap the rear edge (30.5) of theelevating shovel. A pair of first hydraulic cylinder piston aggregates(40) are provided to activate the telescoping bars (38), whichaggregates (40) lie beneath their associated telescoping bars and, likethem, are arranged so as to be slightly inclined downward towards therear relative to the horizontal. Both ends of the cylinders (40.1) ofthe first aggregates are connected with the fixed portions (38.1) of thetelescoping bars (38). Bolts (42) are placed on the forwardly projectingends of the piston rods (40.2) of the first aggregates, which bolts (42)extend through respective longitudinal slots formed in the smoothunderside of the associated fixed portion (38.1) in one of thetelescoping bars, and are mounted in the front end of the associatedmovable portion (38.2) of this telescoping bar.

For folding and extending the chassis (10) while raising or lowering thefolding axis (36), a pair of second hydraulic cylinder piston aggregates(44) is provided, which extend approximately horizontally rearward onboth sides of the tractor from the center of the engine (28) to just infront of the folding axis (36) and are hinged at the front to the frontportion (10.1) of the chassis and at the back to the rear portion (10.2)of the chassis, which extends forward beyond the interrupted axis (36)to the engine (28), so that the upper second aggregates (44) engage therear portion (10.2) of the chassis approximately over the folding axis(36), which is arranged approximately at the level of the supportsurface (30.3) of the elevating shovel at its front end.

The front of the recess (32) in the rear portion (10.2) of the chassisis defined by two holding arms (46) that lie lateral to the longitudinalaxis (18) of the tractor, are partially rigidly connected with eachother, are formed identically as roller blocks having two parallelrollers (46.1), and are mounted so as to rotate about a horizontallateral axis (46.2) on the free ends of the piston rods (48.1) of a pairof third hydraulic cylinder-piston aggregates (48), the cylinders (48.2)of which are horizontally attached to the front portion (10.1) of thechassis at the level between the first and second aggregates (40 and44). The holding arms (46), consequently, can be moved between a forwardposition above the front end of the support surface (30.4) of theelevating shovel and a rear position in front of the rear edge (30.5) ofthe elevating shovel.

On each of the two rear end sections (38.2.1) of the movable telescopingbar elements (38.2) there is formed an eye (50) which projects towardthe plane of symmetry containing the longitudinal axis (18) of thetractor. A truncated shaft (52) is mounted on each such eye (50) in sucha manner that its rotational axis perpendicularly crosses thelongitudinal axis of the associated telescoping bar (38), i.e., runsapproximately vertical. A pulling arm (54), in turn, in the form of aroller block having two rollers (54.1) is attached to each truncatedshaft (52) and is mounted so as to rotate about an axis whichperpendicularly intersects the axis of the associated truncated shaft(52), whereby each pulling arm (54) can be pivoted out of a releaseposition parallel to the bar axis into a blocking position lateral tothe longitudinal axis (18) of the tractor and back, independently of thecondition of the associated telescoping bar (38). For this purpose apair of fourth hydraulic cylinder-piston aggregates (56) is provided,which are functionally arranged between the respective pulling arms (54)and the movable portions (38.2) of the telescoping bars associatedtherewith. While the front end of the cylinder (56.1) of each fourthaggregate (56) is hinged to the smooth underside of the associatedmovable telescoping bar element (38.2), the free end of the piston rod(56.2) of the fourth aggregate projecting rearwardly approximately inthe longitudinal direction of the telescoping bar (38) is hinged to acorner of an essentially triangular, flat, one-armed lever (58), whichis pivotably mounted at another corner to the underside of thetelescoping bar portion (38.2). At the third corner of this triangular,flat one-armed lever (58), a flat, rigid coupling member (60) is hingedto the underside of the element (38.2) of the telescoping bar, which, inturn, is hinged to this underside at the free end of a flat pivot arm(62), which is attached to the lower end of the associated truncatedshaft (52). The axes of all such hinged joints, which in the given orderconnect the piston rod (56.2), the one-armed lever (58), the couplingmember (60) and the pivot arm (62) with each other, are arrangedparallel to the axis of the truncated shaft (52).

All of the hydraulic aggregates are reversible and are subjected topressure by means of an hydraulic pump connected to the engine (28). Therequisite fluid lines and control and regulating elements must beprovided.

The loading and raising of the nose landing gear (not shown) of anairplane that is to be maneuvered without a tow bar takes place in themanner described below.

Beginning condition of the tractor: By maximum extension of the secondaggregate (44), the chassis (10) is extended; by maximum reduction ofthe first aggregate (40), the two-piece telescoping bars (38) are fullyextended, so that their end sections (38.2.1) are located at the rearend of the rear portion (10.2) of the chassis; by maximum extension ofthe third aggregate (48) the holding arms (46) are arranged at the rearend of the elevating shovel (30); and by maximum reduction of the fourthaggregate (56) the two pulling arms (54) are pivoted out of the chassisrecess (32).

In this condition the tractor travels backward until each of the twoholding arms (46) contacts one of the two nose wheels of the unbrakednose landing gear, which at this moment is already between the twohalves of the rear portion (10.2) of the chassis in the rear half of therecess (32), which is always downwardly open. Subsequently, thestill-extended chassis (10) of the stationary, not yet braked tractor isfolded downward in the center by a gradual shortening of the secondaggregate (44), until the support surface (30.1) of the elevating shovelcontacts the tarmac (20); thus causing the wheel axes (24 and 26) tocome closer together. After the placement of the elevating shovel (30)on the tarmac (20), the tractor's brakes are set, whereupon the twopulling arms (54), by maximum extension of the fourth aggregates (56),are pivoted into the chassis recess (32) as the rear closure thereof,and the first aggregates (40) are then extended until the pulling arms(54) contact the back of the nose wheels. The first aggregates (40) arethen gradually extended to further shorten the telescoping bars (38) andsimultaneously the third aggregates (48) are shortened to the samedegree as the telescoping bars, whereby the nose wheels of the airplaneon its unbraked landing gear roll forward over and past the rear edge(30.5) of the elevating shovel, while rolling against the roller blocks(46.1 and 54.1) on the support surface (30.1) to a certain holding line,where they are blocked by the aggregates (40 and 48). Then the foldedchassis (10) is extended by means of a gradual extension of the secondaggregate (44), whereby the elevating shovel (30) moves upward and thenose landing gear of the airplane resting on its support surface (30.1)is raised. After releasing its brakes, the tractor can then be put intomotion and the airplane can be maneuvered.

To lower and unload the nose landing gear, the above-described measuresare performed in the reverse order.

The claims and the abstract are components of the specification.

I claim:
 1. A tractor for maneuvering an airplane without a tow bar,comprising: a chassis (10) having a central longitudinal axis (18) whichchassis includes a rearwardly, upwardly and downwardly open recess (32),a rear portion (10.2) that is forked due to the recess (32) and has apair of coaxially mounted, powered rear wheels (22) mounted on a rearaxle (24), and a front portion (10.1) having two steerable and perhapspowered front wheels (14); a pair of approximately horizontal cylinders(40.1) of a pair of first hydraulic cylinder piston aggregates (40) thatare arranged parallel to each other on the chassis (10) and are foradjusting the length of two telescoping bars (38) each having a fixedportion (38.1) and a movable portion (38.2) which bars are adjustableparallel to the respective side walls (10.2.1) and (10.2.2) of therecess (32) and are each provided at their free rear ends (38.2.1) witha hinged pulling arm (54), which can pivot through a right angle betweena relatively open position relative to the free end (38.2.1) of the barparallel to the axis of the bar (38) and a relatively closed blockingposition perpendicular to the axis of the tractor about a vertical axiswhich perpendicularly intersects the associated bar axis (of 38); asupport surface (30.3) which is arranged on the chassis (10) at thefront end of its recess (38) and is inclined downward toward the rear toallow for the elevation of the nose landing gear when the pulling arms(54) and shortened telescoping bars (38) are in their blockingpositions; and an elevating device including a pair of second hydrauliccylinder-piston aggregates (44) arranged on the chassis (10) for liftingthe nose landing gear after it has been placed adjacent to and on thesupport surface (30.3) and locked in place thereby means of the pullingarms moving into their blocking positions, wherein the front and rearportions (10.1 and 10.2) of the chassis (10) are distinct units and areconnected with each other in an articulated manner by means of a singlefolding axis (36) running parallel to the rear axle (24); the secondaggregates (44) arranged approximately horizontal parallel to thetractor axis (18) are hinged at one end to the front portion (10.2) ofthe chassis (10) and at the other end to the rear portion (10.2)thereof; the cylinders (40.1) of the first aggregates (40) and the fixedportions (38.1) of the telescoping bars (38) are mounted to the frontportion (10.1) of the chassis (10) and an elevating shovel (30) havingthe support surface (30.3) is attached to this front portion (10.1)behind the folding axis (36); and a pair of approximately horizontalcylinders (48.2) of a third cylinder-piston aggregate (48) is providedarranged on the front portion (10.1) of the chassis (10), the pistonrods (48.1) of which are arranged adjustably on the respective two sides(10.2.1 and 10.2.2) of the recess (32) in the chassis (10) and areprovided at their free rear ends with at least one holder (46) which ishinged perpendicularly to the tractor axis (18) and always projects intothe recess (32) in the chassis (10).
 2. Tractor according to claim 1,wherein the folding axis (36) is arranged approximately at the level ofthe support surface (30.3) of the elevating shovel (30) near the frontend thereof, and the second aggregate (44) engages approximately abovethe folding axis (36) with the rear portion (10.2) of the chassis (10).3. Tractor according to claim 1, wherein the telescoping bars (38) andthe first aggregates which adjust them are inclined from the horizontal(18) so as to be downwardly inclined toward the rear.
 4. Tractoraccording to claim 1, wherein the cylinders (40.1) of the firstaggregates (40) and the fixed portions (38.1) of the telescoping bars(38) are arranged in pairs adjacent to one another in such a manner thatone cylinder (40.1) and one fixed rear portion (38.1) of the telescopingbars (38) are arranged on each side in the recess (32) in the chassis(10) at points that are approximately diametrically opposite each otherrelative to the tractor axis (18), and in that the one-sided piston rods(40.2) of the first aggregates (40), which project forward out of theassociated cylinders (40.1), engage at the front ends of the movablefront portions (38.2) of the telescoping bars (38).
 5. Tractor accordingto claim 1, wherein for the mounting of the pulling arms (54),respective truncated shafts (52) are provided on the free ends (38.2.1)of the movable end portions of the telescoping bars (3), which truncatedshafts extend along the pivot axis of the associated pulling arm (54)and are rotatably mounted on the end of the associated telescoping bar(38.2.1), and for the pivoting of the pulling arms (54), respectivepivot arms (62) connected with the associated truncated shaft (52) so asto rotate therewith and cylinders (56.1) of a pair of fourth hydrauliccylinder-piston aggregates (56) mounted on the associated movableportion of the telescoping bar (38.2) are provided, the piston rods(56.2) of which cylinders (56.1) project rearwardly out of saidcylinders (56.1) and are hingedly coupled with the end of the associatedpivot arm (62) opposite the respective truncated shafts.
 6. Tractoraccording to claim 5, wherein each fourth aggregate (56) is arranged onthe movable end portion (38.2) of an associated telescoping bar (38)approximately parallel to the other fourth aggregate, and the front endof its cylinder (56.1) is hinged there, and its piston rod (56.2) ishingedly connected to a triangular one-armed lever (58), one end ofwhich is pivotably mounted on the end portion (38.2.1) of thetelescoping bar, at a point lying closer to the pivot axis of the lever(58); and in that one end of a rigid coupling member (60) is hinged tothe other end of the lever (58) at a point lying further away from itspixot axis, and the other end of the coupling member (60) is hinged tothe free end of the associated pivot arm (62), whereby all hinge axesare parallel to each other and to the pivot axes of the associatedpulling arms (54), as well as being approximately vertical.
 7. Tractoraccording to claim 1, wherein the pulling arms (54) and holders (46) areeach formed as roller blocks which are mounted on the associatedtruncated shafts (52) and on the respective free rear ends of the pistonrods (48.1) of the associated third aggregate (48), respectively, insuch a manner as to be able to freely rotate on their axes (54.2 ,46.2), which may be permanently or only sometimes horizontal.
 8. Tractoraccording to claim 1, wherein the holders are formed as holding arms(46) and are partially rigidly connected with each other laterally withrespect to the tractor axis (18).